The present invention relates generally to a dynamic behavior control apparatus for an automotive vehicle, and more specifically, to a method and apparatus for controlling the roll characteristics of the vehicle by changing a brake force distribution.
Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the roll over characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
Vehicle rollover and tilt control (or body roll) are distinguishable dynamic characteristics. Tilt control maintains the vehicle body on a plane or nearly on a plane parallel to the road surface. Roll over control is maintaining the vehicle wheels on the road surface. One system of tilt control is described in U.S. Pat. No. 5,869,943. The ""943 patent uses the combination of yaw control and tilt control to maintain the vehicle body horizontal while turning. The system is used in conjunction with the front outside wheels only. To control tilt, a brake force is applied to the front outside wheels of a turn. One problem with the application of a brake force to only the front wheels is that the cornering ability of the vehicle may be reduced. Another disadvantage of the system is that the yaw control system is used to trigger the tilt control system. During certain vehicle maneuvers, the vehicle may not be in a turning or yawing condition but may be in a rollover condition. Such a system does not address preventing rollover in a vehicle.
It would therefore be desirable to provide a roll stability system that detects a potential rollover condition as well as to provide a system not dependent upon a yaw condition.
It is therefore an object of the invention to provide a roll control system for use in a vehicle that is not dependent upon the turning condition of the vehicle.
In one aspect of the invention, stability control system for an automotive vehicle includes a plurality of sensors sensing the dynamic conditions of the vehicle and a controller that controls a distributed brake force to reduce a tire moment so the net moment of the vehicle is counter to the roll direction. The sensors include a speed sensor, a lateral acceleration sensor, a longitudinal acceleration sensor, a roll rate sensor, and a yaw rate sensor. A controller is coupled to the speed sensor, the lateral acceleration sensor, the roll rate sensor, the yaw rate sensor. The controller determines a roll angle estimate in response to lateral acceleration, roll rate, vehicle speed, and yaw rate. The controller determines a brake force distribution in response to the relative roll angle estimate. The controller may also use a pitch rate to determine the roll angle estimate.
In a further aspect of the invention, a method of controlling roll stability of the vehicle comprises the steps of:
determining a roll angle estimate in response to lateral acceleration, longitudinal acceleration, roll rate, vehicle speed, and yaw rate; and
determining a brake force distribution in response to the relative roll angle estimate.
One advantage of the invention is that the turning radius of the vehicle is not affected by the roll stability control.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.